If the user has generated the appropriate authentication
credentials (e.g., obtaining Kerberos tickets), the
frontend/backend authentication process is handled by PQexec without any further intervention. The
following routines may be called by libpq
programs to tailor the behavior of the authentication process.

fe_getauthname Returns a pointer to
static space containing whatever name the user has
authenticated. Use of this routine in place of calls to
getenv(3) or getpwuid(3) by applications is highly recommended,
as it is entirely possible that the authenticated user name is
not the same as value of the USER environment variable or the
user's entry in /etc/passwd.

char *fe_getauthname(char* errorMessage)

fe_setauthsvc Specifies that
libpq should use authentication
service name rather than its compiled-in default. This value is
typically taken from a command-line switch.

void fe_setauthsvc(char *name,
char* errorMessage)

Any error messages from the authentication attempts are
returned in the errorMessage argument.